1. Field of the Invention
The present invention relates generally to the field of radar apparatus and, more particularly, to electric signal synchronization apparatus or circuits used in radar and other electronic equipment, the operation of which is controlled by electronic synchronization signals.
2. Discussion of Related Art
Radars, like many other electronic systems have dramatically increased in performance, complexity and cost over the past several decades. The driving forces for radar improvement have included greatly expanded air traffic since the end of World War II and the new and increasingly sophisticated military weapon systems for and against which modern radars are required to operate. At the same time, the substantial radar improvements have been made possible by technical advancements in such fields as computers, microelectronics and materials.
Along with important improvements in radar performance, an increased need has arisen for improved radar reliability and rather cost control, the latter becoming especially important as military budgets receive closer governmental and public scrutiny. The costs of radar systems, as for other electronic systems, reflect not only procurement costs for the systems but also the cost of spare parts and maintenance and repair costs.
Radar systems, to which the present invention is principally but not exclusively directed, are known to be comprised of several different subsystems and components. Principal of these subsystems and components are the transmitting and receiving antenna, usually integrated into a single antenna or antenna assembly; a microwave transmitter; a transmitter exciter; a return signal receiver; a duplexer; a receiver protector; a return signal processor and a synchronizer. Various of these radar subsystems and components may, of course, be physically integrated so as to be packaged in a common housing or housings. Nevertheless, the general functions can still be considered as being separate.
It can be readily appreciated that, during normal radar operation, different subsystems are required to perform different functions at different operating intervals (that is, clocks). Generally, these functions vary with time, but may usually be repetitive over longer periods of time. As an example, an antenna may, during rotation, change its angular pointing direction; however, the same rotational positions are repeated each time the antenna is rotated through 360.degree.. Therefore, in some radar systems the antenna sweep period may establish the repetitive functions of some components. Also, some or all of the functions may change as the operating mode is changed, for example, in some radar systems, between search and track modes.
In a typical radar system, each repetitive operating cycle is divided into a large number, such as 64,000, of very short time intervals which are commonly referred to as pulses or counts. At specific counts in each cycle, specific events are required to occur which collectively define or control operation of the radar system. Accordingly, the operation of the radar system can be defined by a schedule of events which are required to occur at specific pulses or counts, it being recognized that at many pulses no events may be required while at other pulses the associated event may involve several different operations.
Assuming that a radar system operation can, in fact, be defined by an event-pulse schedule, it is the principal function of the synchronizer to provide controlling or implementing signals to the proper system components at the proper pulse counts. As a result, the synchronizers are required to have the capabity for handling the entire number of pulses per cycle (range) and to provide for numerous, often simultaneous, outputs of control or implementing signals (events).
The usual manner of implementing a typical synchronizer has heretofore been to provide a memory having a number of memory locations equal to the number of pulses in a range for each funcitonal output. Typically, this has involved the use of large numbers of random access memories (RAMs) with a large number of output addresses. For a 16,000 (16K) count system having 16 outputs, about 20 conventional integrated circuits have, for example, been required. For 64K count system having 16 outputs, the integrated circuit count typically increases to 68. Accommodating such numbers of integrated circuits requires a number of printed circuit boards (PCBs).
The use of such large numbers of integrated circuits to implement syncrhonizers increases system parts and assembly costs and also increases the size and weight of electronic portions of the radar system, an important consideration for airborne and many mobile radar systems. Moreover, the large number of circuits and PCBs required increases the logistical costs associated with providing and stocking adequate replacements parts. Still further, as is commonly known, reliability tends to decrease as the parts count increases, due to the general statistical nature of malfunctions or failures.
Also, it can be appreciated that even more complex radars, in current prototype, design or conception stages, are expected to increase the performance requirements of synchronizers, thereby tending to further increase the size, weight and cost of the synchronization and reduce their maintainability and reliability. Therefore, to offset such new requirements for more complex synchronizers for new generation radars, as well as to reduce costs, size and weight of present generation radars, improvements to synchronizers are needed to reduce the parts count and provide more efficient operation.